The other two main tributaries of Pearl River are theDong River (literally, the East River) andBei River (the Northern River). As for other functions, it plays a vital role in carbon storage and transport in Southern China.[5] The Xi River is facing some ecological challenges such asdrought,[6]invasive species,[7] andpollution.[8]
The basin of the Xi River ranges from easternYunnan Province to southernGuangdong Province with a humid subtropical or tropical monsoon climate.[6] The Xi River is navigable for its entire length. It is a commercial waterway of southern China, and links thedelta cities to the interior. Over two thousand years ago, theLingqu Canal was dug, connecting the Xi River basin (theLi River, which is a tributary of theGui River) with theXiang River, which flows into theYangtze, thus providing a continuous waterway from thePearl River Delta to theYangtze Valley. The Xi River is rich in water conservancy and water resources, providing significant contributions to agriculturalirrigation, river transportation, andpower generation in coastal areas.[6]
The Xi River is the largest of the Pearl's tributaries. Its volume of flow is second in China only to that of theYangtze River, and it supplies water to many places in Guangxi, Guangdong and Macau. The greater Xi River is also one of China's longest. Existing in many segments it extends for 2,271.8 km (1,411.6 mi):
Nanpan River: 950 km (590 mi)
Hongshui River: 669.6 km (416.1 mi)
Qian River: 121.0 km (75.2 mi)
Xun River: 172.2 km (107.0 mi)
Xi River (including main branch to the sea): 359.0 km (223.1 mi)
Xijiang river system (italics referring to rivers flowing outside ofGuangxi)
Rivers are a significant storage and transport system for both organic and inorganic carbon.[9] The Xi River is an important source of atmosphericcarbon dioxide in Southern China, with carbon inputs coming mainly from the river's headwaterNanpan andBeipan rivers. In the Beipan River, carbon inputs come from the oxidation of organic carbon and the coal industry along the river. In the Nanpan River, carbon inputs come mainly from soil and organic detritus.[5]
The Xi River basin has historically experienced droughts, which are worsening due toclimate change and rapidurbanization along with many parts of the river. This increase in population is straining water resources. The climate of the watershed issubtropical totropical monsoon, with 80% ofprecipitation falling between April and September.[6] This extreme variation in yearly precipitation patterns exacerbates drought issues. Climate change is predicted to cause a significant decrease in average, highest, and lowest river flows, with average flow droppings anywhere from 4 to 49%.[6] Increasing frequency and severity lead the meteorological and hydrological droughts.
Invasive ornon-native species are an issue in rivers in southern China, including the Xi River.[7] Southern China rears the majority of non-native species inaquaculture.[7] These species are mainly introduced from aquaculture, and maypredate oroutcompetenative species.[7] Most introduced species areomnivores, including theNile tilapia, the most common non-native species in southern China rivers.[7]
Many commercial fish species in the Xi River and the encompassing Pearl River watershed have been contaminated with significant amounts ofBisphenol A, common in plastics manufacturing.[10] Bisphenol A is a chemical that can be harmful to theendocrine system of fish and humans.[10]
In order to protect the Xi River, theGuangxi Zhuang Autonomous Region government issued a notice prohibiting new construction projects and migration of people within the land occupied andinundated areas of the Xi River mainstream control project in Guangxi.[11] Besides, the protection measures include: promulgated afishing ban,[12]wetland park protection, develop greenrecycling and low-carbon economic, the innovation of ecological andenvironmental protection cooperation mechanism and Xi River Basin Nature Reserve construction management.[13]